REDUCTION OF ENERGY DEMAND IN PAPER MAKING USING ONLINE OPTIMISATION AND CONTROL

造纸是一个能源密集型行业：即使是一个小规模的造纸厂，每年也可以使用超过150 GWh的能源，相当于一个中等规模的城镇。英国有50多家造纸米尔斯，年产量超过500万吨纸和纸板。造纸米尔斯生产的产品范围从精美的纸张到瓦楞纸板，并涉及具有不同特性的各种过程的融合，其中突出的是，非最小相位，批量，多变量，时滞和非线性系统。该过程由按顺序排列的若干部分组成。整个生产线的控制一般由分散控制系统（DCS）实现。因此，该工厂具有复杂的多层控制系统，每层混合了先进的，经典的和手动的回路。此外，造纸机是一个混合系统，结合湿部和干部，这代表了间歇和连续过程的混合物。在本项目中，在建立分段过程模型的同时，还将利用热力学原理（能量平衡和熵流等）和沿着造纸生产线控制系统提供的过程数据建立能流模型。期望能量流模型将揭示整个过程中的能量分布，并且分段能量消耗将与控制变量（即，控制回路设定点）和其它部分操作变量。一旦工厂的过程和能量流模型可用，它们就可以通过在线动态优化和通过模型预测控制（MPC）技术进行控制来用于热能管理。在这种情况下，MPC可以用来实现产品质量，生产和能源效率方面的多优化目标。目前，MPC已用于实时优化（RTO），以便在过程级为控制回路生成适当的设定点，并将单个性能函数与过程约束一起使用。目前，多个目标可以通过在执行优化之前指定它们的相对偏好来并入MPC算法。然而，随着成本/能源消耗随时间的变化，这种偏好信息将动态变化，一系列可行的质量/效率的权衡应明确提供给过程supervisers.Based上，本研究的结果简单易用的建模和信息呈现系统将被开发。该系统将与参与该项目的工业合作伙伴合作开发，并将用于执行集成过程监测，控制和优化示范过程，以证明所开发方法的有效性。在线闭环实时多变量节能MPC控制系统也将在两台造纸机上实施：1。SK SSK纸板机是同类机器中的典型：纸张排水中发生自然的不受控制的变化，并导致进入干燥机的纸张的固体含量发生变化。进入干燥器的纸页的固体含量越高，需要越多的蒸汽来干燥纸页。2.另一方面，在Aylesford，与能源供应商签订的合同约束工厂每天使用固定数量的蒸汽。提高热效率将导致蒸汽必须被倾倒，除非增加产量以使用备用蒸汽。

Paper making is an energy-intensive industry: even a small scale paper mill can use in excess of 150GWh of energy per year, as much as a medium-sized town. There are more than 50 paper mills in the UK with annual production of more then 5 million tonnes of paper and board. Paper mills produce products which range from fine papers to corrugated cardboard and involves fusion of a variety of processes with different characteristics, prominent amongst which are, non-minimum phase, batch, multivariable, time-delay and nonlinear system. The process consists of a number of sections arranged in a sequential way. The control of the whole production line is generally realized by distributed control systems (DCS). As such the plant has complex multilayered control systems with mixture of advanced, classical and manual loops in each layer. Moreover, paper-making machine is a hybrid system, combining wet end and dry end, which represents a mixture of batch and continuous processes. In this project, in parallel to the sectional process modelling, energy flow models will be established using principles in thermal dynamics (energy balance and entropy flow etc) and the process data available from the control systems along the paper making production line. It is expected that the energy flow models will reveal the energy distribution in the entire process and the sectional energy consumptions will be dynamically linked with control variables (i.e., control loop set points) and other sectional operational variables. As soon as the process and energy flow models of the plant are available, they can be used for the thermal energy management via online dynamic optimisation and control via model predictive control (MPC) techniques. In this context, MPC can be used to realize multi-optimization objectives in terms product quality, production and energy efficiency. At present, MPC has been used for real-time optimization (RTO) so as to generate appropriate set points to the control loops at the process level, and single performance function has been used together with process constraints. At present, multiple objectives can be incorporated into MPC algorithms via specifying their relative preferences prior to the optimization being performed. However, as the cost/energy consumption changes with time, this preference information will change dynamically and a range of feasible quality/efficiently trade-offs should be explicitly made available to the process supervisors.Based on the results of this research simple-to-use modelling and information presentation systems will be developed. The system will be developed in collaboration with the industrial partners involved in the project and will be applied to perform integrated process monitoring, control and optimisation of the exemplar processes to demonstrate the effectiveness of the developed methodologies. An online closed loop real-time multivariable energy-reducing MPC control system will also be implemented on two of the paper machines:1. The SK SSK board machine is typical of its kind: natural unregulated variations in sheet drainage occur and cause variations in the solids content of the sheet entering the dryer. The higher the solids content of the sheet entering the dryer, the more steam is required to dry the sheet. 2. On the other hand, at Aylesford, a contract with the energy supplier binds the mill to take a fixed quantity of steam each day. Improved thermal efficiency would result in steam having to be dumped unless production was increased to use the spare steam.